Ios UIView转换为UIImage时如何使用自动布局

CPOAnnotationView是UIView的子视图，我想将CPOAnnotationView转换为UIImage

- (UIImage*)getImage:(CPOAnnotationViewSize)size {
    CPOAnnotationView* annotationView = [[CPOAnnotationView alloc] initWithFrame:CGRectZero];
    [annotationView setNeedsLayout];
    [annotationView layoutIfNeeded];
    
    CGSize s = annotationView.bounds.size;

    UIGraphicsBeginImageContextWithOptions(s, NO, [UIScreen mainScreen].scale);
    [annotationView.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage*image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

问题是CPOAnnotationView具有灵活的宽度，可以包装其内容。因此，我将CPOAnnotationView的框架设置为CGRectZero。我搜索stackoverflow，有些人说如果你想把uiview转换成uiimage。uiview的宽度或高度不得为零。但我的CPOAnnotationView具有灵活的宽度，在设置帧之前计算宽度很复杂。以下是CPOAnnotationView的代码

- (instancetype)initWithFrame:(CGRect)frame{
    if (self = [super initWithFrame:frame]){
        self.translatesAutoresizingMaskIntoConstraints = NO;
        
        _titleView = [[UIView alloc] initWithFrame:CGRectZero];
        _titleView.translatesAutoresizingMaskIntoConstraints = NO;
        _titleView.backgroundColor = [UIColor whiteColor];
        [_titleView layoutIfNeeded];
        [self addSubview:_titleView];
        
        NSMutableArray* titleViewConstraints = [NSMutableArray arrayWithCapacity:0];
        [titleViewConstraints addObject:[NSLayoutConstraint constraintWithItem:_titleView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeCenterX multiplier:1.0f constant:0.0f]];
        [titleViewConstraints addObject:[NSLayoutConstraint constraintWithItem:_titleView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0f constant:34.0f]];
//        [titleViewConstraints addObject:[NSLayoutConstraint constraintWithItem:_nameLabel attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:_avatarButton attribute:NSLayoutAttributeRight multiplier:1.0f constant:kInnerMesListCellAvatarRightMargin]];
//        [titleViewConstraints addObject:[NSLayoutConstraint constraintWithItem:_nameLabel attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:_dateLabel attribute:NSLayoutAttributeLeft multiplier:1.0f constant:-10.0]];
        [self addConstraints:titleViewConstraints];
        
        UILabel* label = [[UILabel alloc] initWithFrame:CGRectZero];
        label.translatesAutoresizingMaskIntoConstraints = NO;
        label.backgroundColor = [UIColor orangeColor];
        label.textAlignment = NSTextAlignmentCenter;
        label.text = @"1000000";
        label.font = [UIFont systemFontOfSize:16];
        label.textColor = [UIColor blackColor];
        [label layoutIfNeeded];
        [_titleView addSubview:label];
        
        NSMutableArray* labelConstraints = [NSMutableArray arrayWithCapacity:0];
        [labelConstraints addObject:[NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:_titleView attribute:NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f]];
        [labelConstraints addObject:[NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:0.0f constant:34.0f]];
        [labelConstraints addObject:[NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:_titleView attribute:NSLayoutAttributeLeft multiplier:1.0f constant:10.0f]];
        [labelConstraints addObject:[NSLayoutConstraint constraintWithItem:label attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:_titleView attribute:NSLayoutAttributeRight multiplier:1.0f constant:-10.0f]];
        [_titleView addConstraints:labelConstraints];
    }
    
    return self;
}

下面是如何调用getImage（）方法，使用getImage（）方法创建地图注释，并将注释添加到地图视图

    CPOAnnotation *annotation = [[CPOAnnotation alloc] initWithCoordinate: coordinate  image:[cpoMarker getImage:CPOAnnotationViewSize_Big] content:[cpoMarker content]];
    [self.mapView addAnnotation:annotation];

并在MapView回调方法调用时向MapView添加注释：

- (MAAnnotationView *)mapView:(MAMapView *)mapView viewForAnnotation:(id<MAAnnotation>)annotation {
   if([annotation isKindOfClass:[CPOAnnotation class]]) {
        CPOAnnotation* cpoAnnotation = annotation;
        NSString *cpoReuseIndetifier = [NSString stringWithFormat:@"%@_%@", @"cpoReuseIndetifier", [cpoAnnotation content]];
        MAAnnotationView *annotationView = [mapView dequeueReusableAnnotationViewWithIdentifier:cpoReuseIndetifier];
        if (annotationView == nil) {
            annotationView = [[MAAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:cpoReuseIndetifier];
        }
        annotationView.image = [cpoAnnotation image];
        return annotationView;
    }
}

-（MAAnnotationView*）地图视图：（MAMapView*）地图视图用于注释：（id）注释{
if（[annotation IsKindof类：[CPOAnnotation类]]）{
CPOAnnotation*CPOAnnotation=注释；
NSString*cpoReuseIndetifier=[NSString stringWithFormat:@“%@”、@“cpoReuseIndetifier”、[CPOAnotation content]]；
MaAnotationView*annotationView=[mapView dequeueReusableAnnotationViewWithIdentifier:CPoreUseIndifier]；
如果（注释视图==nil）{
annotationView=[[MAAnnotationView alloc]initWithAnnotation:annotation reuseIdentifier:CPoreUseIndifier]；
}
annotationView.image=[cpoannotationimage]；
返回注释视图；
}
}